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Today: Chapter 8 – Angular Momentum Chapter 9 – Work and Kine<c Energy
Nov 16, 2015 LB 273, Physics I Prof. Vashti Sawtelle Prof. Leanne Doughty
Irish Phrasebook
auldfella and auld wan – your father and mother
Torque and Angular Momentum
τnet = dL/dt
Discuss It!
How can you explain Alex’s change in angular momentum if the system includes everything?
Exam 3
• When? – Monday 23rd
• What’s on it? – ConservaJon of momentum – RotaJonal moJon – Energy
• Review – Materials on LON-‐CAPA – Extra office hours
-‐ Thursday 19th 5:30pm-‐8:30pm -‐ Friday 20th 1:00pm-‐4:00pm
Announcements
• LON-‐CAPA HW for Ch 9 & Ch 10 due Friday 20th
• On-‐paper HW due on Monday 23rd – This will help you prepare for Exam 3
Review session for final exam (Exam is Dec. 18th, alternaJve to be scheduled soon)
A. Thursday 10th at 7pm B. Friday 11th at 5pm C. Saturday 12th at 2pm E. Other
TBD!
Ch 9 – Work & KineJc Energy
Foothold ideas: Kinetic Energy and Work
• Newton’s laws tell us how velocity changes. The Work-Energy theorem tells us how speed (independent of direction) changes.
• Kinetic energy = • Work-energy theorem tells us how the
kinetic energy will change as a result of exerting an external force
221 mv
W = ΔKE
Foothold ideas: Kinetic Energy and Work
• So how do we relate this idea of work back to forces?
• The dot product here tells us that direcJon magers; which we know.
• Work done by a force (part of force || to displacement)
WF = F � Δr
WF = F � Δr or F!Δr
Each row in the following table pairs a force vector with a corresponding displacement resulting in work W being done. In which of these rows is the work done zero?
A.
B.
C.
D.
E.
�
Δ r
�
F
Each row in the following table pairs a force vector with a corresponding displacement resulting in work W being done. In which of these rows is the work done zero?
A.
B.
C.
D.
E.
�
Δ r
�
F
The force and the direcJon of the displacement vector are perpendicular so the work done is 0.
Each row in the following table pairs a force vector with a corresponding displacement resulting in work W being done. In which of these rows is the work done positive?
A.
B.
C.
D.
E.
�
Δ r
�
F
Each row in the following table pairs a force vector with a corresponding displacement resulting in work W being done. In which of these rows is the work done positive?
A.
B.
C.
D.
E.
�
Δ r
�
F
The force and the direcJon of the displacement vector are in the same direcJon – so the work is posiJve.
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